Manufacture of portland cement



Sept. 17, 1929 P. T. LINDHARD 1,728,496

MANUFACTURE OF PORTLAND CEMENT Filed Nov. 11, 1927 ii 9 I Wi WIN Portland cement,

pass a -mesh sieve.

16 ground to this de ree of fineness being 20"carrying on the grinding to such 'an extent '25 ness.- It has also been found that special ent invention, it has been found that such '40 in the final grinding.

uniformity in the quality of the cement fi raw Patented Sept. 17, 1929 x POVL T. LINDHARD, 0F BROOKLYN, vNEW 'YOR K, ASSIGNOR TO I, L. SMIDTH &; 00., OF

NEW YORK, N. Y., A CORPORATION OF NEW JERSEY MANUEACT'U'IRJE 0F PORTLAND CEMENT Application filed November 11, 1927. Serial No. 232,519.

als

This invention is concerned particularly with the production of what is known in the cement industry as special Portland cement. In the manufacture of standard the cement clinker, with the addition of the proper percentage of raw gypsum, is reduced in a preliminary grinding to such a degree of fineness that approximately 90% of the material will The material round to this fineness is then subjected to a further grinding, by which it is reduced to such a degree of fineness that approximately 80% will pass a 200-mesh sievefithe material cri int

known as standard Portland cement, or Portland cement of standard fineness. It has been found that certain desirable characteristics of the cement can be secured by that approximately 98% of the material will pass a QOO-mesh sieve, the materialthus produced being known' as special Portland cement, or Portland cement of special finecal tin Portland cemen t, although made from standard Portland cement of uniform qual-. ity, is sometimes subject to variations in quality. In the development of the presto variation in quality of special Portland cement is due to the loss by the raw gypsum of some of its water of crystallization and its conse uent conversion into plaster of Paris. ot only does the desirable uni- Pa formity of the product sufi'er by reason of res the varying extent to which the raw gypsum is converted into plaster of Paris, but the economy of production also suffers because the grinding bodies are coated with a pelliclo of fine material, which material reduces the capacity of the grinding apparatus and makes it, necessary to reduce the feed of material. The lack of T0 at manifests itself in the behavior of the finished material, particularly with regard to the setting time, which may change considerably with the varying conversion of gypsum into plaster of Paris. Ithas ter ture of the material in the ing above what is referred to herein as the ture at which the tween 125 F. and 150 the energy is partly converted into heat, which is manufacture'of standard Portland cement, the increase of temperature of the material thus brought about .the added heat, is

temperature of the material above the criticement 'quality,'if none of the raw converted into plaster of Paris.

manufacture o expended is 80 the standard fineness, material is increased to .a degree about or above the critical temperature, with the conversion of the raw gypsum to plaster of the product. Th invention has been to 0 been found that the variation in quality the finished ris, is due to the raising of the temperaprocess of grindtical temperature, that is, the temperaraw gypsum is converted o plaster of Paris, this critical temperature being about 240 F.

The cement I clinker is ordinarily delivered the grinding mill at a temperature of beimparted to the material. In the by the grinding, that is, not suflicient to raise the degree above mentioned and the standard produced is therefore of a uniform gypsum has been In the conued grindin of the material for the F special cement, the energy probably increased as much as and if the heat thus developed is added the heat of the material as it comes from grinding mill in which it is reduced to the temperature of the ris to a greater or less extent, and corponding variations in"the uniformity of e purpose in view in this prevent such variation the product due to the conversion of the rawgypsum to plaster of Paris by reason of a raising of the temperature of the material above the critical degree in the grinding.

this end the temperature of the material or after the grinding to standard cement neness is reduced to a degree below that at which the heat added in subsequent grindmg would raise the temperature ofthe maial above such critical degree, the grinding of the material to special cement fineness being. then carried on.

material, by reason of the conversion of the raw gypsum to plaster of F. In the grinding,

a to the mill 0, no

The invention can be practised with apparatus of various forms, the grinding mills being of any suitable character and the devices for reducing the temperature of the material being likewise of such a character as may be suited to the preference of the manufacturer or the conditions under which the manufacturer is carried on, and being either independent of the grinding mills or incorporated with one or the other.

In the accompanying drawings, in which are illustrated different forms of apparatus adapted for the practise of the invention:

Figure 1 is an outline view in sectional elevation showing the cooling device interposed between two grinding mills" Figure 2 is a view in sectional elevation showing the cooling device incorporated with one of the mills.

In the embodiment of the invention illustrated in Figure 1, there is indicated at a a portion of a grinding mill of ordinary constructiomirom which the cement material reduced therein to standard fineness, that is, such fineness that about 80% will pass a 200-mesh sieve, is delivered to a conveydn b. The temperature attained by the material in the grinding mill (1, if the clinker is properly cooled and the grinding is carired on under proper conditions, will ordinarily be from 200 F. to 240 F. If the material from the'mill a, at or near the temperature stated, were delivered directly which the material is reduced to special cement fineness, that is, to a fineness such that about 98% will pass a 200- mesh sieve, in which reduction the energy expended is probably increased by about 80%, the heat imparted to the material, added to the temperature of from 200 F. to 240 F., would raise the temperature of the material to a degree considerably higher than 240 F., which may be taken as the critical temperature at which the conversion of raw gypsum into plaster of Paris begins, the conversion progressing with the increase of temperature. Furthermore, under such conditions the grinding bodies in the second mill would become coated with a pe'llicle of fine material with the result of loss of efficiency and reduction in capacity of the mill. Such reduction in capacity would make it necessary to reduce the feed to the mill, with a consequent increase in the transmission of heat to the material, whereby the conversion of raw gypsum into plaster of Paris would be further promoted and the quality of the finished product further aflected.

For the purpose of reducing the temperature of the material at the standard fineness so that its temperature shall not be raised above the criticaldegree by the reduction to special cement fineness, the con-veyor b, in the embodiment of the invention illustrated in Figure 1, is made to deliver the material masses of standard fineness to a cooler d, from which it is in turn delivered to the mill 0. The cooler cl may be of any suitable construction. As shown in Figure 1, it is a tubular cooler in which the cement moves upward through tubes cl in a shell (2 which is supplied with cooling water adn'iitted at e and discharged at ef, Below the lower tube sheet d isa chamber f, in which is placed a mechanical mixer f and to which is supplied air, as indicated at f f whereby the cement material is reduced to a condition of fluidity and, being constantly supplied by the conveyor f, is made to flow upward through the tubes d tube sheet (i the cement material flows out through a chute or conduit (i directly into the second mill 0. I

In the passage of the material through the cooler d, the temperature of the material is 5 reduced to such a degree that the heat added to the material by the grinding to a special cement fineness in the Il'llll'C will not raise the temperature of the material above the the conversion 9 critical temperature at which of raw gypsum into plaster of Paris would take place. If, for example, it is assumed that the temperature of the material of standard fineness is 240 F. and that, under operating conditions, there is an increase of 9:,

100 F. in the reduction of the material to a special cement fineness, the temperature of the material would be raised to 340 F., which is much above the critical temperature at which the conversion of raw gypsum takes 100 place. By the cooling of the cement material, which can be regulated by regulation of the flow of cooling water through the cooler, the temperature of the material ofstandard fineness is reduced to such a degree, say F., that the heat added in the fine grinding will not raise the temperature of the material to the critical degree. The

conversion of raw gypsum to plaster of Paris will therefore be wholly rcvented and 10 the finished product will there ore be of uniform quality.

Obviously the prevention of the heating of the material above the critical temperature might be accomplished by incorporation of 5 cooling devices with one or the other of the grinding mills. Such an embodiment of the invention is illustrated in Figure 2, in which the shell 1 of the mill is shown as jacketed by an outer left between the two shells, to which water may be supplied by a pipe g which, with a suitable joint and stufling box, passes centrally through the feeding trunnion g of the mill and is connected through pipes g car-. 125

ried by the head of the mill, with the water space g Through similar pipes and at discharge pipe 9' ccntrally placed in the delivery trunnion g of the mill, the water which has absorbed heat from the mill and of the cooler cl." From the upper shell g, a space being 120 the material in the mill is discharged. By

such means the temperature of the material may be reduced or kept below the critical temperature and the conversion of raw gypsum into plaster of Paris avoided.

It will be seen that the invention, so far as it finds expression in the method of grinding cement material, can be practised in various forms of apparatus. a 1 I claim as my invention:

1. The method of grinding Portland cement material to special cement fineness, which consists in grinding the cement material to standard cement fineness, reducing the temperature of the material to a degree below that at which the heat added in subsequent grinding will not raise the temperature of the material above the critical degree of change of quality, and then grinding the material to special cement fineness.

2. The method of grinding Portland cement material to special cement fineness, which consists in rinding the cement material to standard Tortland cement fineness,

subsequently cooling the material to a degree such that the heat added in subsequent grinding will not raise the temperature of the material above the critical degree of change of quality, and then grinding the material to special cement fineness.

This specification signed this 2nd day of Nov. A. D. 1927 POVL T. LINDHARD. 

